The invention relates to a locking nail for fracture fixation.
Locking nails to care for bone fractures are well known. See, for example, U.S. Pat. No. 5,312,406. These nails are inserted into the medullar space in the bone canal which was prepared or bored open and are inserted from the proximal or distal end of the bone. The nails are locked in the bone, in case of femoral fractures with cross-locking screws. Interlocking is performed by passing bone screws through cross-bores at the ends of the nail shank. This causes the locking nail to axially hold the bone components together and also keeps the bone segments from rotating.
Such locking nails have become known, for example, from U.S. Pat. No. 4,622,959. Further, it is known to employ such locking nails for the guidance and retention of femoral neck screws as has become known, for example, from U.S. Pat. No. 5,176,681 and EP 0 321 170 or German Utility Model G 85 28 770 U1.
Finally, it also has become known to provide such locking nails with a device to allow compression as has become known from German patent DE 35 41 597 or U.S. Pat. No. 4,281,649, the teaching of which is incorporated herein by reference. The proximal end of the locking nail mostly has an elongate cross-bore, and a female thread is provided in the hollow end portion of the nail shank to receive a compression screw with the aid of which the bone screw may be displaced in the elongate cross-bore in parallel with its axis.
It is the object of the invention to improve a compression type locking nail to the effect that it has an improved locking performance despite its compressive characteristic.
In the locking nail of the present invention a second cross-bore for a bone screw is provided between the elongate cross-bore and the end of the nail shank facing it. In addition, the female thread for the locking member is between the elongate cross-bore and the second cross-bore and the distance between bores and the length of the locking member are chosen to be such that the locking member allows the passage of a bone screw through the second cross-bore even when the bone screw is at the end or close to the end of the elongate cross-bore which faces the near end of the nail shank or the second cross-bore. After the nail is inserted and the cross-bores are found in the bone canal by means of an aiming apparatus, the bone screw for the elongate cross-bore will be inserted as well. Its position expediently is such as to enable the bone screw in the elongate cross-bore to be displaced in parallel with itself or axially with the nail subsequently with the aid of the locking member. This causes compression at the point of fracture. After this operation is completed another bone screw may be passed through the second cross-bore and the nail may be appropriately locked.
The second cross-bore, at the end of the nail shank, leaves sufficient space for another female thread into which the aiming apparatus and/or a drive-in and extraction instrument may be screwed.
From the previously mentioned EP 0 321 170 and U.S. Pat. No. 5,176,681, the teaching of which is incorporated herein by reference, it has already been known to provide two threaded portions on the nail shank of a locking nail to pass through a femoral neck screw. The threaded portion which is placed more inwardly serves for positioning a securing screw by which the femoral neck screw is kept from rotating. The outer threaded portion serves for receiving the aiming apparatus or a drive-in or extraction instrument.
According to an aspect of the invention for a tibia nail, the axis of the second cross-bore is offset from the axis of the elongate cross-bore by an angle which preferably is 90xc2x0.